1. Field of the Invention
The present invention relates to a hydroprocessing catalyst and its use in the hydroprocessing of heavy hydrocarbon oils.
2. Prior Art
The present invention relates to a catalyst suitable for the hydroprocessing of heavy hydrocarbon oils, in particular hydrocarbon oils containing relatively large amounts of vacuum residue fraction. These oils contain a large amount of impurities such as sulfur, Conradson carbon residue (CCR), metals, nitrogen, and asphaltene, and it is needed to effect hydrodesulfurisation (HDS), carbon residue reduction (HDCCR), hydrodemetallisation (HDM), hydrodenitrification (HDN), asphaltene reduction (HDAsp) and/or conversion into lighter products. The present invention also relates to a process for hydroprocessing heavy hydrocarbon oils, in particular feeds containing substantial amounts of vacuum residue using said catalyst.
Hydrocarbon oils containing 50 wt % or more of components with a boiling point of 538° C. or higher are called heavy hydrocarbon oils. These include atmospheric residue (AR), of which at least 50 wt. % boils above 538° C., and vacuum residue (VR), of which at least 90% boils above 538° C. It is desired to remove impurities such as sulfur from these heavy hydrocarbon oils by hydroprocessing, and to convert them into lighter oils, which have a higher economic value.
Various catalysts have been proposed for this purpose in the art. Generally, these catalysts are capable of efficiently removing sulfur, Conradson carbon residue (CCR), various metals, nitrogen and/or asphaltenes. However, it was found that the decomposition of asphaltenes is generally accompanied by the formation of sediment and sludge. Sediment can be determined by the Shell hot filtration solid test (SHFST). (see Van Kerknoort et al., J. Inst. Pet., 37, p. 596 604 (1951)). Its ordinary content is said to be about 0.19 to 1 wt. % in product with a boiling point of 340° C. or higher collected from the bottom of a flash drum.
Sediment formed during hydroprocessing may settle and deposit in such apparatuses as heat exchangers and reactors, and because it threatens to close off the passage, it may seriously hamper the operation of these apparatuses.
The formation of sediment is a particular problem in the hydroprocessing of feeds containing a relatively large amount of vacuum residue fraction. There is therefore need for a hydroprocessing catalyst which is particularly suitable for removal of sulfur, metals, and Conradson carbon from these feedstocks, which generally have at least 80 wt. % boiling above 538° C., while at the same time effecting high conversion into products boiling below 538° C., and showing low sediment formation.
Japanese Patent Laid-Open No. 1994-88081 discloses a hydroprocessing method for heavy hydrocarbon oils by using a catalyst with a specific pore size distribution. In this method a catalyst is used with 3 to 6 wt. % of a Group VIII metal oxide, 4.5 to 24 wt. % of a Group VIB metal oxide, and 0 to 6 wt. % of phosphorus oxides loaded onto a porous alumina carrier which has a specific surface area of 165 to 230 m2/g, a total pore volume of 0.5 to 0.8 ml/g, and a pore size distribution wherein 5% or less of the total pore volume is present in pores with a diameter less than 80 Å, 65–70% of the total pore volume present in pores with a diameter below 250 Å is present in a range of 20 Å below the MPD to 20 Å above the MPD, and 22–29% of the total pore volume is present in pores with a diameter of more than 250 Å.
However, although this method can achieve efficient hydrodesulfurisation and Conradson carbon reduction, it does not solve the problem of sediment formation.
Japanese Patent Laid-Open No. 1994-200261 discloses a hydroprocessing method for heavy oils, and a catalyst used to implement this method. In this reference a catalyst was proposed with 2.2 to 6 wt. % of a Group VIII metal oxide and 7 to 24 wt. % of a Group VIB metal oxide on a porous alumina carrier, which catalyst has a surface area of 150–240 m2/g, a total pore volume of 0.7 to 0.98 ml/g, and a pore size distribution wherein less than 20% of the total pore volume is present in pores with a diameter less than 100 Å, at least 34% of the total pore volume is present in pores with a diameter of 100–200 Å, and 26–46% of the total pore volume is present in pores with a diameter of more than 200 Å. However, this catalyst does not show a sufficient decrease in sediment formation.
Japanese patent publication 2-48485 describes a process for preparing an alumina catalyst carrier which has 0.6 to 0.85 ml/g of its pore volume in pores with a diameter below 500 Å and 0.1 to 0.3 ml/g of pore volume in pores with a diameter of 1000 to 10000 Å. The pore mode in the range up to 500 Å is 90–210 Å. The U-value, defined as D50/(D95-D5), is at least 0.55. The macropore volume of this carrier is very high, making it difficult to maintain stable hydrodesulfurization activity. Additionally, this reference gives no indication on how and in what form the alumina described therein can be applied in hydroprocessing.
U.S. Pat. No. 4,395,329 describes a hydroprocessing catalyst for heavy oils which has a specific pore size distribution. The catalysts described in this reference have 10–25% of pore volume present in pores with a diameter above 10000 Å. Especially when these catalysts are made by extrusion, this will detrimentally affect the strength of the catalyst and it is expected that it will be difficult to use the catalyst commercially.
U.S. Pat. No. 5,322,829 describes an ebullated bed catalyst which may comprise 0.1–5 wt. % of nickel, calculated as oxide, and 1–15 wt. % of molybdenum, calculated as oxide, wherein the catalyst has a surface area of at least 150 m2/g and a total pore volume of 0.8–1.4 ml. The carrier has at least 0.4 cc/g of pore volume in pores with a radius below 200 Å. However, it can be assumed that the catalyst based on the carrier described in this reference has less than 50% of its the total pore volume present in pores with a diameter of at least 200 Å. Therefore, the diffusion of ultraheavy fractions into the pores will be insufficient.
U.S. Pat. No. 4,414,141 is directed to a hydrotreating catalyst suitable for the hydrotreating of heavy feedstocks. The catalyst generally has a total pore volume 0.75–0.95 ml/g and a surface area generally is 150–300 m2/g. It has 0.25–0.40 ml/g of pore volume in pores with a diameter below 250 Å, 0.1–0.25 ml/g of pore volume in pores with a diameter of 250–500 Å, 0.20–0.30 ml/g in pores with a diameter of 500–1500 Å, 0.05–0.15 ml/g in pores with a diameter of 1500–4000 Å, and 0.03–0.1 ml/g of pore volume in pores with a diameter above 400 Å. The catalyst is indicated to be suitable for HDS. No indication is given on the activity of the catalyst in metals removal or asphaltene removal.
Canadian patent No. 1248513 describes a HDS/HDM catalyst suitable for heavy hydrocarbon feeds. The catalyst has a total pore volume of at least 0.5 ml/g, a compacted density of at least 0.4 g/ml, a macropore volume of 0.035–0.075 ml per ml of catalyst volume, and a micropore volume of at least 70% of the nitrogen adsorption volume and at least 0.12 ml/ml of catalyst volume. The reference gives no information on asphaltene removal or sediment formation. Additionally, most of the catalysts in this reference have a very high pore volume. At a pore volume of more than 1.0 ml/g, catalyst strength is often insufficient.